Experiments on the effect of histamine in burn, tourniquet, and endotoxin shock in mice suggested that endogenous histamine is not a lethal factor in burn and tourniquet shock, but rather it appears to have a compensatory, beneficial effect. Studies on the number and function of T and B cells from the spleens of normal and burned mice indicated that the decreased numbers and mitotic activity of T cells could play a role in the impaired cellular immunity after burns, but the same findings in B cells could not be critical in the development of normal humoral immunity in the absence of an overwhelming infection after thermal trauma. In other experiments, various vasoactive hormones were studied on their effect upon swelling produced by a mild vacuum applied to the mouse tail. Compensatory mechanisms are such that inhibition of swelling results in most cases, even with capillary dilators.